This invention relates to a process for preparing a synthetic wood product.
It is known that an elongated foamed article can be prepared by extruding a normally hard, thermoplastic resin from a die while in a softened state. If a die having a single orifice and which is normally used for the preparation of a board is employed, however, the elongated article obtained does not have a structure wherein foamed portions of high density exist alternately with foamed portions of low density. The foamed article does not have, therefore, a ring structure as seen in natural wood. The foamed articles obtained by these conventional processes although not having appearance which actually resembles natural wood, are sometimes called synthetic wood.
A process is also known for preparing a foamed structure in which foamed portions of higher density are contained therein alternately with foamed portions of lower density, both portion extending throughout the entire structure. In the process a foamable resin is extruded through a die provided with a number of apertures and mounted on an extruder to form a number of foamed resin strands, each of which has a high density surface skin and a low density inner portion, which strands are different in their average densities. The strands are then coalesced into a unitary foamed article. In the foamed article thus obtained, each of the strands acts as if it were one annual ring, and as a result, the foamed article shows a property similar to natural wood. Such a process is disclosed in Japanese Patent Publications No. 47-40293, No. 47-40294 and No. 47-51945 and U.S. Pat. No. 3720572.
Because the synthetic wood obtained by the above process has a structure wherein a number of foamed strands, having various average densities, are coalesced, density differences are provided even in the inner portions. Thus, the synthetic wood has an appearance of straight grains and mechanical properties resembling natural wood. Further, characteristically the straight grains do not disappear even with planing off or other fabrications. Due to such advantages, the synthetic wood has a wide variety of applications in many fields.
The synthetic wood described above, however, sometimes has disadvantages when used in certain specific applications. For example, the synthetic wood is easily torn away along the coalesced surfaces formed between the foamed strands therein, and thus the synthetic wood has a low bending strength in the direction perpendicular to the longitudinal direction of the strands. As a result, when the synthetic wood is made into a broad board, it is not suitable for use in applications wherein bending strength may be needed in the width direction of the board. A need exists, therefore, for a synthetic wood having an appearance of straight grains on the surface thereof and a high bending strength in the width direction. The present invention has been made in order to meet the above need.